Perovskite AMoO₃ (A = Ca, Sr, Ba): A New Ambient-Stable and Water-Soluble Sacrificial Layer Family for Single-Crystal Self-Supporting Oxide Membrane Fabrication

Development of self-supporting oxide membrane fabrication using a sacrificial layer method has attracted great attention over the past decade, specifically for their promising integration as devices on silicon and flexible substrates due to their large panel of properties such as ferroelectricity, ferromagnetism, superconductivity, and metal/insulator transition. Known sacrificial layer materials with a perovskite-related structure, such as La_<i>x</i>Sr_1-<i>x</i>MnO₃ and YBa₂Cu₃O₇, are dissolved in acidic or basic solutions. To prevent oxide membranes from being attacked by the sacrificial layer dissolution solution, it is important to find perovskite water-soluble sacrificial buffers. In this work, we evidence the perovskite molybdates AMoO₃ (A = Ca, Sr, Ba) as a new ambient-stable and efficient water-soluble sacrificial layer family for the fabrication of oxide membranes. We first show the stability in an ambient environment of CaMoO₃, SrMoO₃, and BaMoO₃ epitaxial films deposited on (001)SrTiO₃ substrates and their water dissolution kinetics with membrane release times longer than the SrVO₃ material and the well-known Sr₃Al₂O₆ sacrificial layer material. We analyze the etching kinetics via operando optical monitoring of the remaining sacrificial layer surface still attached to the initial template substrate. We found for the molybdate family a first-order reaction kinetics with a main exponential decay, with constants, respectively, of around 11 h, 14 h, and 19 h for CaMoO₃, SrMoO₃, and BaMoO₃. We use this molybdate family to release an 80 nm-thick SrTiO₃ membrane on a polydimethylsiloxane support with a smooth morphology observed by atomic force microscopy and a monocrystalline quality observed by high-resolution X-ray diffraction. These results open a range of pseudocubic lattice parameters of the ambient-stable and water-soluble sacrificial buffers with pseudocubic lattice parameters from 3.90 to 4.04 Å for self-supporting perovskite oxide monocrystalline membrane fabrication.